The problem of design, and how evolutionary biologists talk about it
I’m really glad my article peaked your interest. As I am English, I do not have a firm idea of what a fifth grader would know (!), but I can try to clarify some aspects of the article that were glossed over. In particular, I think that if you can grasp what I called the ‘reflexive’ narrative then everything else falls into place (at least to some extent). Here, I am going to take re-explanation in a broad sense so you can get a feel for the logical steps in the argument. I apologise if parts of this are trespassing on firm ground, but hopefully you can indulge me. In response to Tam Hunt, I am going to provide a more concise set of principles that may also be of interest.
Ever since the dawn of history, written records have shown a fascination with the order and apparent purpose that is found within nature (often within religious or philosophical themes). In Western Christian traditions, the design in nature was often used as an argument in favour of the existence of God(s) because an atheist would have to plead some miraculous process of creation to describe where this design came from. The existence of God seems a very human and natural thing to suppose because we live in intimately constructed environments where we ourselves act as designers and creators of order. As such, it is easy to sympathise with the logic that design necessitates a Creator.
This is really the starting point for both in the history and in the theory of evolution by natural selection. When Charles Darwin was young, he greatly admired the teleological argument (i.e. the argument for God from design) of William Paley, which is epitomised by Paley’s now-famous watchmaker passage. But, after experiencing both the diversity and similarity of living things around the world during the voyage of the Beagle, Darwin became convinced that there must be some natural explanation for design in nature (i.e. not supernatural involving Gods as Creators). Natural selection was developed as akin to ‘artificial selection’, which is the process by which human breeders modify the appearance of domestic plants and animals: instead of a breeder selecting which individuals shall breed or not based on their features, Nature (or the environment) takes on the role of the breeder in selecting which individuals successfully reproduce (so pass on their heritable material to offspring, which we now know to be genes) and which do not.
By taking this approach, the outstanding question is: What traits does natural selection preserve? A human breeder is free to select any trait that is found within a population of individuals based on their aesthetic preferences, which has led to an astounding diversity of features in domestic species (just look at dogs, cats, roses and so on). If there is natural selection, Nature must have some similar aesthetic preference that chooses between existing variations of features within a population. Darwin called this natural preference ‘fitness’ — arguing that Nature preserves individuals that suit their environments. This may seem trivial or obvious, but you have to remember that there were other competing theories at the time that had different conceptions of the direction of change between generations.
Across evolutionary biologists, there exists a wide range of opinions as to whether Darwin’s argument in ‘The Origin of Species’ is basically unchanged in current theory, incomplete with several key omissions or just downright wrong. These disputes are generally not very interesting because each way of phrasing Darwin’s contribution is stating the same facts in a different narrative that gives more or less sympathy to the scientific and technological limitations of Darwin’s era. The important point is that 1) we have a problem to be explained of ‘design in nature’ and 2) we have a solution that is ‘natural selection’.
What I was trying to point out in ‘The Structure of Evolutionary Theory — in Pictures’ was that there exists three distinct correct-and-consistent narratives that explain what natural selection does within evolutionary theory (but I will only focus on one here). The basic problem is that biological phenomena can be described at different levels. This is not something that is unique to biology, but (and this may well be very rare if not unique) there is a real need for cross-level explanation to make intuitive sense of the relationship between ‘design in nature’ and ‘natural selection’. The challenge is that natural selection acts on whole organisms, effecting their adaptation via differential survival and reproduction. But the organisms’ themselves die each generation and only genes are passed on. And, as each organism contains many thousands of genes, natural selection only chooses which genes are passed on between generations very indirectly (say, rather than comparing each one on its own).
The result is astounding. If we echo the same question that Darwin was driving at and ask ‘What does natural selection preserve?’ but in the context of genes and organisms, we find out that organisms are naturally selected to maximise the contribution of their genes to future generations. You can see this in remarkable examples of adaptation that involve one organism being altruistic to another (that is, accepting a cost to itself to benefit another). For example, in many social insects like ants, bees and wasps, individuals may forgo reproduction in order to help another individual to reproduce. This can maximise the contribution of an individual’s genes to future generations if the altruist and the recipient of the altruism share genes. This was the key insight from William Hamilton (and others) that was never clearly established by Darwin.
So, the design of organisms, which are complex assemblages of thousands of genes, is intimately related to genes that underlie their features. From this, we get the idea of a ‘reflexive’ process where genes build organisms, organisms interact with the environment and the genes that survive between generations change. As a consequence, the design of organisms in one generation may differ from another, and the process continues on… (The other two narratives focus on describing gene change without reference to organisms, and organism change without reference to genes.)
If you can follow me this far, then it may also be possible to understand the real cutting-edge of evolutionary research. Although it is true to say that each of the three narratives can correctly describe evolutionary change, they do not make the same predictions. Intuitively, this is the same problem that physicists encountered with the transition from Newtonian to Einsteinian mechanics, and evolutionary theory is currently in need of its Einstein!
Currently, we have some rules-of-thumb for working out which narrative to use to make predictions within particular problems, but we do not understand how the narratives gel together. To be explicit, there is no reason from the study of gene change why organisms exist in the first place! Why should genes cooperate together? What prevents organisms from being pulled apart by selfish genes? What makes organism’s the focus of adaptation? When do groups become the focus of adaptation? Why don’t gene interactions produce a chaotic assemblage of higher-level traits?
To do answer questions like these, we need some meta-narrative that links all three of the strands together in some intuitive manner. This is a really exciting area of research, as was evidence by the great popularity of this fundamental question at a recent conference of European evolutionary biologists (which I was proud to attend). Sadly, because of academic politics, I cannot describe my very-minor contributions to resolving these questions until publishing the research in a peer-reviewed journal. But, if you are interested, I can recommend some further reading of books and articles that I have found fascinating.
I don’t know if any of that helped or not, but if you have any queries I would love to hear from you. Thanks again for reading and responding!